Electrophotographic imaging devices, such as laser printers, fax machines, and photocopiers, are designed to produce a desired image on a print media, such as a sheet of copy paper. Electrostatic imaging devices generally include a photoconductive element that is selectively illuminated by a scanned laser beam or a light emitting diode array in response to data representative of the desired image that is to be produced, wherein the incident light generates an electrostatic copy of the desired image on the photoconductive element. The photoconductive element is then exposed to toner powder that adheres to the electrostatic copy of the desired image and is subsequently transferred from the photoconductive element to the print media. A fuser unit then fuses the “loose” toner powder to the print media.
Fuser units typically employ a combination of heat and pressure to fuse the toner powder to the print media. A fusing unit may employ a pair of opposing rollers that form a fusing nip, with one roller serving as a fuser roller and the other roller serving as a pressure roller. The fuser roller generally contacts the un-fused toner, while the pressure roller applies a pressure, or nip force, at the fusing nip to hold the print media in contact with the fuser roller. The fuser roller is generally heated while the pressure roller may or may not be heated. To fuse the looser toner to the print media, a fuser motor rotates the fuser and pressure rollers in a forward direction causing the print media to be drawn through the fusing nip, at which point the combination of pressure and heat from the rollers melts the loose toner and permanently affixes it to the print media.
The fusing nip force can significantly impact print quality. For example, if the pressure between the fuser and pressure rollers is too light, heat transfer from the fuser roller to the toner powder will be poor and the toner power will not adequately bond to the print media and cause the printed image to deteriorate. Therefore, to improve heat transfer to the toner powder, fuser units may maintain high pressure between the pressure and fuser rollers and utilize pressure rollers made of a compliant material or having an elastomeric outer layer. Unfortunately, the surfaces of these types of pressure rollers are susceptible to potentially deforming thermal sets if allowed to stay in contact with the fuser roller when an imaging device loses power and the fuser unit cools down from normal operating temperatures ranging between 150° C. to 200° C. Such thermal sets are often in the form of a flat spot on the surface of the pressure roller that can thereafter generate print defects and, thus, reduce print quality.